Fighting a battle with Amazon.com Inc. to be the preferred entry point for Internet shopping, Google Inc. last year retooled its lucrative search page. Its strategy is showing signs of progress.

The change allowed retailers to post pictures, descriptions and prices of products at the top of search results, both on desktop computers and, later, mobile devices. For example, a Google search for "microwave oven" shows a grid of photos for specific models, sold online by retailers like Macy's Inc. and Target Corp.,...